Water inhibits CO oxidation on gold cations in the gas phase. Structures and binding energies of the sequential addition of CO, H ₂ O, O ₂ , and N ₂ onto Au ⁺

and water. The current experiments and calculations might lead to a molecular level understanding of the interactions between the active sites, reactants and impurities which could pave the way for the design of efficient nanocatalysts.